Hummel K
Z Rechtsmed. 1987;98(2):111-8. doi: 10.1007/BF00200467.
A "realistic" prior probability is always based on case experience (Akten-a-priori). In serological opinions pertaining to parentage, the realistic prior probability is only one piece of information in the whole body of evidence before the judge and does not have any special significance per se. There is no such thing as a "neutral" prior probability. It either implies "ignorance," in which case it cannot be "information," or it must be taken in connection with the utility principle, in which case it is not a "probability." The utility principle is defined in law and cannot be expressed in figures. The utility principle takes effect only when the judge reaches a decision (on the basis of all the evidence before him). It determines the relative importance of the participant's objects of legal protection which are at issue in the case. The expert is bound to apply a neutral utility component, i.e., in a two-hypothesis case (the normal situation) the significance of both the null and the counter hypothesis must carry the same weight. A null and/or a counter hypothesis can combine several single hypotheses; the mean value of their frequencies is taken. As a rule, one should avoid using a "prior case probability" ("Akten-a-priori") when calculating a W value. An "expectation of error" should be as realistic as possible and hence be obtained using a "prior case probability."
“现实的”先验概率总是基于案例经验（案件先验）。在亲子鉴定的血清学意见中，现实的先验概率只是法官所掌握的全部证据中的一项信息，其本身并无特殊意义。不存在“中立的”先验概率这回事。它要么意味着“无知”，在这种情况下它不可能是“信息”，要么它必须与效用原则相关联，在这种情况下它就不是“概率”。效用原则在法律中有明确规定，无法用数字来表达。效用原则只有在法官做出裁决（基于其面前的所有证据）时才会生效。它决定了案件中所涉及的参与者受法律保护对象的相对重要性。专家必须应用一个中立的效用成分，也就是说，在双假设情形（正常情况）下，原假设和对立假设的重要性必须具有同等权重。一个原假设和/或一个对立假设可以合并几个单一假设；取它们频率的平均值。通常，在计算W值时应避免使用“先前案例概率”（“案件先验”）。“误差预期”应尽可能现实，因此应通过“先前案例概率”来获得。
